Effects of method, duration, and sleep stage on rebounds from sleep deprivation in the rat

Total sleep deprivation (TSD) of rats for 24 hours or less by continually e nforced locomotion has consistently produced subsequent rebounds of slow-wa ve or high-amplitude EEG activity in NREM sleep, which has contributed to t he widely held view that this EEG activity reflects particularly "intense" or restorative sleep. These rebounds usually have been accompanied by subst antial rebounds of REM sleep. In contrast, chronic TSD (2 weeks or longer) by the disk-over-water (DOW) method has produced only huge, long-lasting re bounds of REM sleep with no rebound of high-amplitude NREM sleep. To evalua te whether the different rebounds result from different methods or from dif ferent lengths of deprivation, rats were subjected to 24-hour TSD by the DO W method. Rebounds included increases in high-amplitude and slow-wave activ ity; ie, the methods produced similar rebound patterns following short-term TSD. (Chronic TSD by continually enforced locomotion would be strategicall y difficult and severely confounded with motor fatigue.) Rats subjected to DOW-TSD for 4 days, well before the development of severe TSD symptoms, sho wed primarily REM sleep rebounds. Rats subjected to 2 day of selective REM sleep deprivation, but not their closely yoked control rats, showed large, significant REM sleep rebounds, which evidently were not induced by the str ess of the deprivation method per se, The combined findings prompted reexam ination of published evidence relevant to "sleep intensity," including "neg ative rebounds, rebounds in other species, the effects of stress and fatigu e, depth of sleep indicators, and extended sleep. The review points out pit falls in the designation of any specific pattern as intense sleep.